Yarn tensioning devices have been provided assuming a wide variety of configurations. Such devices are extremely important because of their many areas of usefulness in the textile industry. Because of complicity of the problems engendered in the tensioning of a moving strand this has become a highly developed art. One type of yarn tension device in common use in textile industry utilizes tensioning disks, a number of pairs of which may be provided in spaced aligned relation, such as exemplified in U.S. Pat. No. 3,132,824. Other tension devices utilize arcuate rotatable elements such as balls. What constitutes substantially a point contact between the rotatable element and the yarn is illustrated in U.S. Pat. Nos. 1,372,557, 1,432,399 and 3,753,535. Because of the point contact, full advantage is not obtained from rotation imparted by yarn movement because of limited contact between the yarn and the ball. The yarn in such instances has the tendency, always following the path of least resistance, to come out from under the ball with consequent irregularities in or loss of tension. The tendency of such devices to pinch the yarn is thought to also produce undesirable results. Where the wrap of the yarn about the rotatable device is excessive, such as illustrated in U.S. Pat. Nos. 1,040,185 and 1,490,512, there is a tendency for the ball to bounce up and down producing irregular tension, and the force of inertia resulting from repeated impacts tending to damage the yarn.
Accordingly, it is an important object of this invention to provide a yarn tension device utilizing a rotatable element in engagement with the yarn which will result in more nearly uniform tension without excessive tendency to pinch the yarn.
Another important object of the invention is to produce a yarn tensioning device which may rely to a greater degree upon the kinematic action of rotating elements wherein the force required to rotate the elements acts to tension the yarn by retarding its forward movement.
Another important object of the invention is to provide a tension device wherein the amount, as well as the mode of application of the tension are subject to a variety of adjustments.
Still another important object of the invention is to provide a yarn tension device having a self-threading feature wherein the yarn may be presented for readily passing under the rotatable elements. Yarn guides may also be provided for maintaining the yarn in such position within a yarn channel.